A110256 Denominators in the fractional coefficients that form the partial quotients of the continued fraction representation of the inverse tangent of 1/x.

1, 1, 4, 9, 64, 225, 256, 245, 16384, 99225, 65536, 480249, 1048576, 1002001, 4194304, 41409225, 1073741824, 2393453205, 4294967296, 4102737925, 68719476736, 940839860961, 274877906944, 4113258565689, 17592186044416

Offset

1,3

Comments

Limit A110255(2*n-1)/a(2*n-1) = limit A110257(n)/A110258(n) = 4/Pi.

Limit A110255(2*n)/a(2*n) = limit A110259(n)/A110260(n) = Pi.

Links

Paul D. Hanna, Table of n, a(n) for n = 1..400

Example

arctan(1/x) = 1/x - 1/(3*x^3) + 1/(5*x^5) - 1/(7*x^7) +-...
= [0; x, 3*x, 5/4*x, 28/9*x, 81/64*x, 704/225*x, 325/256*x,
768/245*x, 20825/16384*x, 311296/99225*x, 83349/65536*x,
1507328/480249*x, 1334025/1048576*x, 3145728/1002001*x,...]
= 1/(x + 1/(3*x + 1/(5/4*x + 1/(28/9*x + 1/(81/64*x +...))))).
The coefficients of x in the even-indexed partial quotients converge to Pi:
{3, 28/9, 704/225, 768/245, 311296/99225, ...}.
The coefficients of x in the odd-indexed partial quotients converge to 4/Pi:
{1, 5/4, 81/64, 325/256, 20825/16384, ...}.

Prog

(PARI) {a(n)=denominator(subst((contfrac( sum(k=0, n, (-1)^k/x^(2*k+1)/(2*k+1)), n+1))[n+1], x, 1))}

Crossrefs

Cf. A110255 (numerators), A110257/A110258 (odd-indexed), A110259/A110260 (even-indexed).

Cf. A095175. [From R. J. Mathar, Aug 18 2008]

Sequence in context: A231812 A069711 A062067 * A095175 A092396 A184877

Adjacent sequences: A110253 A110254 A110255 * A110257 A110258 A110259

Keyword

cofr,frac,nonn

Author

Paul D. Hanna, Jul 18 2005

Status

approved